This invention relates to primer compositions useful in small arms ammunition and the like.
The priming composition in small arms primers is a discrete chemical system, as well as an integral part of the unit generally known as the primer. The small arms primer consists of a cup, an anvil and the priming composition. The cup serves as a container for both the composition and the anvil and generally possesses standard dimensions for fit with the case pocket of various types of small arms cases.
Typically, in manufacture of a primer, the cup is charged with wet priming composition which is thereafter dried to give a resultant dry composition weight of only a few milligrams. A paper disc may be placed on the composition and the anvil pressed into the open end of the cup. Primers fitted with anvils are known in the ammunition industry as Boxer primers. A second type of primer known as the Berdan primer consists of only the cup, the composition and a seal over the surface of the composition.
Boxer primers must be used with ammunition wherein the pocket is a cylindrical well in the cartridge case head. A flash hole is located between the case pocket and the main portion of the case where the propellant is loaded. Berdan primers are for exclusive use with ammunition wherein the pocket is a cylindrical well with a centrally located anvil integral to the case. A pair of flash holes are located on each side of the anvil. The ignition process in either the Boxer or Berdan priming system is similar except that the former results in one gas jet and the latter results in two.
Ignition of a primer is initiated by impact of a weapon firing pin against the central portion of the cup. This mechanical energy deforms the cup, compressing the priming composition against the anvil. Resulting areas of heat in the rapidly compressed composition cause it to ignite almost instantaneously and burn at a very high rate. The ejecta of the combustion reaction, consisting of hot particles and gases, are typically directed to the propellant by means of the flash holes in the base of the case pocket.
The priming composition used for small arms primers must possess sensitivity to impact or mechanical shock. This sensitivity is generally measured by dropping a weight at various distances onto a firing pin situated over the test primer. Typically, groups of 50 primers are tested at different drop heights until data for the group is obtained to predict no-fire, 50% fire, and all-fire levels for the primer. SAAMI (Sporting Arms and Ammunition Manufacturers Institute) specifications for small pistol primer sensitivity are: no function below an one inch fall of the test weight and all-fire at an eleven inch or greater fall, using a 1.94 oz. ball weight. A number of factors are involved in producing such sensitivity levels, but clearly, the priming composition is the most critical. Generally, priming compositions contain a primary explosive--a chemical compound which is impact sensitive. The primary explosive in almost all cases must be modified because it is too powerful or its velocity of detonation is too high. The modification to the effects of the primary explosive is accomplished by the addition of other chemical ingredients which may function as fuels, oxidizers or other agents in the chemical system.
Historically, a number of primer compositions have found use in small arms primers. Over a period of time, most of these have been replaced. For example, mercurous compositions possessed undesirable shelf-life, and along with various chlorates, were found to cause gun barrel erosion. But, since they met the difficult sensitivity and ignition requirements, they were used until improvements were found.
The primary explosive lead styphnate replaced the earlier compounds during WWII, and was the advent of the non-corrosive priming mixtures. These were all based on lead styphnate with various combinations of tetracene, aluminum, antimony sulfide, calcium silicate, lead peroxide, boron, pyrophoric metals and barium nitrate. Variations in ingredients and their relative amounts resulted in chemical systems which possessed sensitivity and propellant ignition properties tailored to specific requirements. These priming compositions have been so reliable that they are, for the most part, still in current use in small arms primers.
Growing concern over environmental hazards and potential effects on individual health, particularly in indoor shooting ranges, has led to investigations and studies of primer exhaust. The occurrence of toxic oxides of lead, barium and antimony, among other exhaust products, from lead styphnate primers has prompted the search for alternate priming compositions by a number of researchers. U.S. Pat. No. 4,608,102 to Krampen et al., owned by the assignee of the present application, for example, relates to a primer composition wherein manganese dioxide and zinc peroxide or strontium peroxide are used as oxidizers in place of barium nitrate. U.S. Pat. No. 4,363,679 relates to a primer composition in which zinc peroxide is the primary oxidizer. These compositions eliminate environmentally hazardous combustion products, but they possess a low flame temperature which, on occasion, creates performance problems.